1. Field of the Invention
This invention relates to a driving process of an enlarged tunnel wherein an ordinary diametrical tunnel is partly made into an enlarged tunnel. More particularly, the invention is directed to a driving process of an enlarged tunnel, wherein a predetermined region of an ordinary diametrical tunnel to be enlarged may be constructed with a direct saving in time and labor as compared to previous methods of constructing an ordinary diametrical tunnel in that predetermined region.
2. Description of Background Art
As for a process for making a part of an ordinary diametrical tunnel into an enlarged tunnel, hithertofore it has been usual that a shaft is excavated from the surface of the ground at a predetermined region to be enlarged of an ordinary diametrical tunnel previously constructed. Various kinds of excavation machines are introduced through the shaft into the ordinary diametrical tunnel and a predetermined region of the ordinary diametrical tunnel is enlarged by an assembled driving machine.
However, this process is defective because in recent years structures on the surface of the ground such as buildings or the like have been increasing. Thus, it is difficult to acquire the land for making the shaft. Additionally, a great deal of trouble is involved with refilling the shaft after the diametrically enlarging work is finished.
The present inventors have previously proposed a driving process of an enlarged tunnel which makes it unnecessary to excavate the shaft. This process is characterized in that, after an ordinary diametrical tunnel is constructed by a primary shield machine, one end portion of a predetermined region to be enlarged of this tunnel is partly excavated, so that an enlarged starting base is established. An enlarging shield machine is assembled in this starting base, and is driven forward, while primary segments which previously lined the whole area of the predetermined region to be enlarged are removed in order. In this manner, the machine proceeds with an enlargement of the tunnel and at the same time an inner surface of the resultant enlarged portion is lined with secondary segments in order so that an enlarged tunnel extending over the predetermined region is constructed.
This proposed process is advantageous because it improves the conventional working efficiency and economical results can be brought about. Additionally, this process shortens the working time and lowers working costs.
However, especially where the region to be enlarged is a comparatively long one, it is desirable to avoid individual or separate work for making the ordinary diametrical tunnel and the work for making the enlarged tunnel.
Accordingly, this invention has for its object to provide a driving process of an enlarged tunnel wherein work for constructing an ordinary diametrical tunnel along the portion that corresponds to a predetermined region to be enlarged can be omitted. Work for making an enlarged tunnel can be carried out directly. The present invention is characterized in that when a primary shield machine is driven along an ordinary diametrical tunnel and reaches a predetermined region to be enlarged, an enlarged starting base is made in the rear of the primary shield machine, and an enlarging shield machine is assembled in the enlarged base. Thereafter the primary shield machine and the enlarging shield machine are both driven through the predetermined region to be enlarged so as to construct the region into an enlarged tunnel.